Issue link: https://www.e-digitaleditions.com/i/1327492
January/February/March 2021 I 55 The connection of an amplifier to the source audio signal should be carefully considered. For typical classrooms and conference rooms, it is often best to use the audio output of the video display or projector. This eliminates the potential mismatch of the audio and video signal processing that takes place in the display device, which can cause delay in the processed video output—resulting in mismatch of the audio and video or a lip-sync issue. Figure 12 shows the recommended connection diagram for this application. Microphone Audio Amplifier Audio Output Video HDMI Signal HDMI Cable Audio Cable Speaker Cable Display / Projector FIGURE 13: Speakers with adjustable output wattage for the needs within a room. In Figure 12, the mixing amplifier accepts the audio from the display or projector and the microphone input, mixing and amplifying the signals to the preset levels powering the speakers. For most conference and meeting rooms and other such areas, a 70 volt amplifier and speaker system should be used to provide full and uniform sound coverage. The audio is mono, not stereo, which improves clarity for the listeners. The high impedance system allows for the use of relatively small gauge wire (16/2) to connect many speakers to a single amplifier. Further- more, 70 volt speakers most often have built-in transformers with multiple taps so that each speaker can be set to a desired output wattage. This allows for adjustment of the sound pressure level (i.e., volume) for various areas within a room or facility, such as public areas versus reception or lounge areas. Figure 13 shows a speaker with an output wattage setting control typically located behind the speaker grille. FIGURE 12: Speaker connection diagram using an amplifier for a conference room or classroom.